Tectonic evolution of Taranaki Basin, offshore New Zealand, The

Abstract

The sedimentary architecture of the Taranaki Basin, located primarily offshore of northwestern New Zealand, reveals the structural and stratigraphic response to the region’s polyphase tectonic history. Using Schlumberger’s Petrel software, 2D and 3D seismic data are structurally and stratigraphically interpreted and depth-converted, and three depth-converted regional cross-sections are sequentially restored through 14 time horizons using Midland Valley’s Move. The structural restoration process incorporates paleobathymetry, isostatic corrections, decompaction, unfaulting, and unfolding, and yields extension and shortening rates from the deepwater to proximal Taranaki Basin. Measured Middle Cretaceous to Paleocene extension rates total 7.0% in the Northern Taranaki Basin, 5.1% in the Central Taranaki Basin, and 1.8% in the Southern Taranaki Basin; the temporal and spatial distribution of extension provides evidence of two-phase rifting. Eocene initiation of Pacific Plate subduction resulted in anomalously high post-rift subsidence, 0.10% shortening across the Northern Taranaki Basin, little to no shortening in the Central Taranaki Basin, and 1.6% shortening across the Southern Taranaki Basin. The Southern Taranaki Basin, which has experienced a higher magnitude of transpressional stress, has seen the greatest variety of shortening-related deformation in the basin. The distribution of strain in the basin is compared with previous research in the region, which reveals that the style of convergence-driven compressional strain is less varied in the Taranaki Basin, where the Taranaki Fault System has accommodated much of the basin shortening, than the nearby Reinga Basin; basement terranes and the spatial relationship between basin location and extinct and active Southwest Pacific subduction zones are presented as the underlying controls on strain distribution. Convergence-related shortening generally occurred in a systematic and sequential manner, migrating north-to-south, and the direction of principal compressive stress has rotated clockwise. Miocene to Recent back-arc extension of 0.44% is measured in the Northern Taranaki Basin, 0.17% in the Central Taranaki Basin, and is not observed in the Southern Taranaki Basin. Extension measured in this study is synthesized with previous research and presented from a rotating block model perspective, demonstrating a general north-south temporal migration of extension. The distribution of ultimate recoverable oil reserves are compared to the areal extent of shortening-related structures in the basin. Approximately 93% of New Zealand’s oil reserves are located within the extent of shortening delineated in this study, and it is proposed that convergence-related structural deformation provides a key control on the distribution of hydrocarbon accumulations in the basin.